Machine for preparing lithographic or other printing plates as well as rubber sheets used in offset printing



Jan. 24, 1950 J. G. LINDMARK MACHINE FOR PREPARING LITHOGRAPHIC OR OTHER PRINTING PLATES AS WELL AS RUBBER SHEETS USED IN OFFSET PRINTING Filed Jan. 25, 1946 2 s t -sheet 1 Jnhan Eur-m a1" Lin :[mark .Jan. 24, 1950 J. G. LINDMARK 2,495,269

MACHINE FOR PREPARING LITHOGRAPHIC OR OTHER PRINTING PLATES AS WELL AS RUBBER SHEETS USED IN OFFSET PRINTING Filed Jan. 25, 1946 2 Sheets-Sheet 2 Johan Gum-Lat Lincffljark Patentecl Jan. 24, 1950 MACHINE FOR- PREPARING LITHOGRAPHIC OR OTHER PRINTING PLATES AS WELL AS RUBBER SHEETS USED IN OFFSET PRINTING Johan Gunnar Lindmark, Stockholm, Sweden, as-

slgnor to Aktiebolaget Johnson & Borsell, Stockholm, Sweden, a corporation of Sweden Application January 25, 1946, Serial No. 643,271 In Sweden January 26, 1945 The present invention relates to the preparation of lithographic or other printing plates as well as of rubber sheets used in the art of oiiset printing.

As is well known, lithographic printing plates of zinc or other material must present, over their entire printing surface, a uniform finer or coarser granulation or grain which is generally obtained by grinding the printing surface. Such a grinding of the plate must be efiected not only when it is desired to prepare an entirely new printing plate, but also an old printing plate, from which the lithographic picture has been washed away, must as a rule be ground again before it can be used anew, particularly if corrections of the old lithographic picture have been effected by grinding with coal or in similar manner.

The grinding of lithographic printing plates has hitherto generally been made by hand or in grinding boxes or similar grinding apparatus filled with sand and water, but such hitherto used grinding methods have been affected with serious inconveniences. In the first instance, the known grinding methods have required far too much time,

The present invention has for its object to provide a machine for preparing the printing surface of lithographic or other printing plates as well as the surface of rubber sheets used in the art of offset printing, by the use of which machine the grinding process may be completed in a considerably shorter time than has been hitherto possible and, furthermore, a surface grain may be readily obtained that is more uniform and better adapted to the requirements in each particular case than the grain obtainable with the old methods. With this and other objects in view there has been provided according to the invention a machine which comprises in combination a rotatable drum, means for clamping the printing plate or rubber sheet onto said drum, and one or more sand blast nozzles directed towards the drum and adapted to be moved back and forth along the same so as to cover the entire printing plate or the like, while ejecting sand or other grinding medium onto the plate or the like.

The accompanying drawing shows, more or less diagrammatically, two embodiments of a blasting machine within the present invention and useful in conducting my process. In this show- Fig. 1 is a vertical longitudinal section through 8 Claims. (Cl. 51-45) a blasting machine made in accordance with my invention,

Fig. 2 is a sectional view, partly in elevation, taken along the line II-II in Fig. 3,

Fig. 3 is a vertical transverse section of the machine taken along the line III-III of Fig. '1,

Fig. 4 is a partial sectional view of a modification, similar to the lower portion of Fig. '2 but showing the use of a pair of blast nozzles,

Fig. 5 is a partial vertical transverse section on a larger scale, similar to the upper portion of Fig. 3, but showing a modification in which sealing means are provided for closing the slot through which the blast nozzles pass, while Fig. 6 is a fragmental sectional view of the modification of Fig. 5, taken along the line 6-6 of this figure.

According to the drawing there is provided in the upper part of a closed housing H! a drum i l, on which a lithographic printing plate 12 of zinc or other material may be secured by means of clamping jaws l3, said drum being rotatably journalled by means of a suitable shaft M, which is driven at a variable speed from an electromotor I5 through the intermediary of a worm-wheel gearing Hi. In one longitudinal wall of the housing right opposite the drum H there is provided a comparatively narrow rectangular opening, which is closed by means of a cylinder or guide 11 journalled in the housing so as to be rotatable around its own axis. Diametrically extending through said cylinder a slot I8 is provided through which a reclprocable sand blast nozzle I9 projects into the housing. The reciprocating movement of the blast nozzle I9 is derived from a longitudinally extending screw spindle 2 0, which is journalled in end plates 2! united with the cylinder l1 and cooperates with a nut 22 which is connected with a holder 23 in which the nozzle I9 is axially displaoeable for the purpose of setting the nozzle at the desired distance from the drum. The screw spindle 20 is driven by means of a worm-wheel gearing or belt drive 25 at a variable speed from an electromotor 24 mounted on the projecting end of the shaft of the cylinder H. For reversing the direction of rotation of the motor 24 and of the screw spindle 20 at the turning points of the nozzle there are provided adjustable limit abutments 26 which change the direction of the rotation of the motor under control of the nozzle by mechanical or electrical means.

It should be clear that by turning the cylinder H and the parts connected therewith about the axis of the cylinder the angle between the envelope surface of the drum I I and the blast nozzle I9 may be adjusted to every suitable value: For locking the cylinder in the adjusted position thereis provided a locking device 21.

The interior of the housing I is in communication with a suction fan or the like through the intermediary of a conduit 28 so that a subatmospheric pressure is always maintained in the machine, whereby dust is prevented from emerging into the workroom. To reduce the air consumption the guide slot I8 for the blast nozzle I9 may be closed by means of an elastic sealing device, for instance consisting of two flexible bands of rubber or the like, as shown at 29' and 30 in Figs. and 6, which bands in their normal position cover the slit opening.

During the sand blasting operation the drum I I is preferably rotated at so high a speed that the' stresses in the printing plate I2 clamped to the drum are increased considerably through the action of the centrifugal force. A drum having a diameter of about 50 centimeters is thus preferablypermitted to rotate at a speed of the order of magnitude of 100 revolutions per minute, corresponding to a peripheral speed of about 260 cm. per second. At the same time the blast nozzle I9 moves slowly at a constant speed back and.

forth along the drum I I and sprays sand or other grinding medium at high velocity against the printing plate I2, which is cleaned by the grind ing efiect of the sand and obtains an evenly grainedsurface, the character of the grain being variable through a suitable selection of the distance of the nozzle from the drum and the direction of the nozzle with respect to the envelope surface thereof and through selection of a suitable sort of sand and a suitable air velocity. Instead of sand another grinding material comparable therewith may be used, of course, for instance saw dust. To avoid patterning, the velocity of movement of the nozzle should be so selected with respect to the speed of rotation of the drum that the nozzle is not periodically directed to exactly the same points of the printing plate.

The invention is, of course, not restricted to the embodiment described above and illustrated on the drawing, but various modifications are conceivable without receding from the inventive idea. Thus there can be used as a driving means for the sand or other grinding medium some other gas than air, for instance nitrogen or some other non-oxidizing gas. Furthermore, the machine may be provided with means for moistening the printing plate or rubber sheet with water or other liquid during the sand blasting operation, as shown at 3| in Fig. 5. It is also possible to employ a plurality of blast nozzles I9, held by holder 23', as shown in Fig. 4 of the drawing. Also other modifications are conceivable.

It should also be clear that as concerns the use of the novel machine for treating the surface of old lithographic printing plates, the machine may be used not only for graining the surface of a printing plate from which the old lithographic picture has been removed by washing with a suitable solvent, but also the removal of the old picture may be effected by sand blasting in the machine.

What is claimed is:

l. A machine for graining lithographic and other printingplates as well as rubber sheets used in the art of oiiset printing, comprising in combination a rotatable drum, means for rotating said drum at a high peripheral speed, means for removably securing the work on said drum,; a

4 housing for said drum, an elongated opening in said housing extending in parallel with the axis of rotation of said drum, elastic sealing members for, said opening, at least one sand blast nozzle extending through said normally sealed opening towards said drum, means for moving said nozzle along said opening while elastically deflecting said sealing means, and suction means communieating with said housing and adapted to maintain a sufficient subatmospheric pressure therein to prevent dust from emerging into the surrounding locality.

2. A machine according to claim 1, in which the elastic sealing-members consist of a pair of flexible bands which in their normal position close the opening.

3. In a machine for graining lithographic and other printing plates as well as rubber sheets used in the art of offset printing, of the type having a work-holding drum adapted to rotate the work at a high peripheral speed througha blast of grinding material, the improvement which comprises -a sand blast nozzle slidable along a.-

guide which is parallel with the drum, said nozzle being rotatable around an axis which is also parallel with the drum.

4. In a machine for graining lithographic and other printing plates as well as rubber sheets used in the art of offset printing, of the type having awork-holding drum adapted to rotate the work at a high peripheral speed through a blast of grinding material, the improvement which comprises a housing for said drum having an elongated opening extending longitudinally of the drum, a

rotatably mounted cylinder covering said elongated opening and having a longitudinal slot therein, at least one sand blast nozzle extendingthrough said opening and directed towards said drum, means for reciprocating said sand blast nozzle along said opening, means for rotatably adjusting said cylinder and blast nozzle andmeans for axially displacing said nozzle to set it.

at the desired distance from said drum.

5. A machine for graining lithographic and other printing plates as well as rubber sheets used in the art of offset printing, comprising in com-;

bination a rotatable drum, means for rotating said drum at a high peripheral speed, means for.

removably securing the work on said drum, a housing for said drum, an elongated opening in said housing extending in parallel with the axis of rotation of said drum, means for sealing said elongated opening, at least one sand blast nozzle extending through said elongated opening and directed towards said drum, means for mov-,; ing said nozzle along said opening while main taining said sealing means operative and suction means communicating with said housing and adapted to maintain a sufiicient sub-atmospheric pressure therein to prevent dust from emerginginto the surrounding locality.

6. A machine for graining lithographic and other printing plates as well as rubber sheetsused in the art of offset printing, comprising in ofrotation of said drum, a cylindrical guide mounted adjacent said opening and parallel therewith, at least one sand blast nozzle mounted on said guide, extending through said elongated opening and directed towards said drum, means.

for moving said'nozzle'slowly and at constant speed along said guide and suction means communicating with said housing and adapted to maintain a suflicient sub-atmospheric pressure therein to prevent dust from emerging into the surrounding locality.

7. The machine of claim 6 wherein additional means are provided for varying the distance of the blast nozzle from the drum.

8. A machine for graining lithographic and other printing plates as well as rubber sheets used in the art of offset printing, comprising in combination a rotatable drum, means for removably securing the work on said drum, a housing for said drum, an elongated opening in said housing extending in parallel with the axis of l6 rotation of said drum, a cylindrical guide mountzle slowly and at constant speed in a reciprocating motion along said guide, and suction means communicating with said housing and adapted to maintain a suflicient sub-atmospheric pressure therein to prevent dust from emerging into the surrounding locality.

JOHAN GUNNAR LINDMARK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 370,987 Stone et al Oct. 4, 1887 1,091,036 Bouillet Mar. 24, 1914 1,476,854 Tilley Dec. 11, 1923 1,940,539 Fritsche Dec. 19, 1933 2,005,654 Fritsche June 18, 1935 2,276,594 Rowell Mar. 17, 1942 2,332,251 Parrish Oct. 19, 1943 

